Management of Methotrexate Toxicity

Introduction to Methotrexate Toxicity Management

The American Academy of Dermatology recommends leucovorin administration immediately at 10 mg/m² every 6 hours, with the dose escalated to 100 mg/m² every 3 hours if severe toxicity develops or methotrexate levels remain dangerously elevated, especially in patients with renal or liver disease 1

Patients with pre-existing renal impairment face a substantially higher risk of methotrexate toxicity, as 85% of methotrexate is renally excreted, and the British Association of Dermatologists recommends avoiding methotrexate entirely in patients with creatinine clearance <20 mL/min 1, 2
Patients with liver disease, such as active or recurrent hepatitis, elevated liver function tests, and chronic liver disease, are at increased risk of methotrexate toxicity 1, 3

The American Academy of Dermatology recommends increasing leucovorin to 10 mg/m² every 6 hours and continuing until recovery if significant clinical toxicity develops, and monitoring complete blood count, renal function, and liver function tests daily 1, 2
For severe toxicity or delayed elimination, the American Academy of Dermatology recommends escalating to leucovorin 100 mg/m² IV every 3 hours until methotrexate level falls below 10⁻⁸ M 1

The Mayo Clinic recommends using higher doses of folic acid and leucovorin as rescue therapy for significant methotrexate toxicities, including painful stomatitis 4

The British Association of Dermatologists recommends daily monitoring of complete blood count with differential to detect worsening cytopenias 1, 2

Leucovorin is most effective when initiated within a few hours of the last methotrexate dose, with efficacy decreasing dramatically as time passes, and becoming doubtful if initiated later than 24 hours after the last methotrexate dose, according to the British Journal of Dermatology 5, 6
Early treatment with leucovorin may be life-saving, particularly given the high mortality risk associated with methotrexate overdose, as recommended by the British Journal of Dermatology 5, 6

If ≥1 mg/kg methotrexate was ingested within 1 hour, give activated charcoal first, then start leucovorin as soon as possible after recognition, as recommended by the British Journal of Dermatology 5, 6
Initial dose of leucovorin: up to 100 mg/m² IV if methotrexate level is unknown, according to the British Journal of Dermatology 5, 6

Admit patients to hospital for monitoring, with aggressive IV hydration (3 L/day) and urinary alkalinization with sodium bicarbonate to maintain urine pH ≥7.0, as recommended by the British Journal of Dermatology 5, 6
Monitor for sepsis, as there is high mortality risk with methotrexate overdose, according to the British Journal of Dermatology 5, 6

Filgrastim (G-CSF) 5 mcg/kg/day subcutaneously may be used for toxic bone marrow suppression to accelerate myeloid recovery, as recommended by the British Journal of Dermatology 5, 6

For accidental intrathecal overdose, oral leucovorin 10 mg may be administered twice daily beginning on the day of treatment and continuing for 3 days to mitigate systemic toxicity, as recommended by the National Comprehensive Cancer Network 7
Leucovorin does not cross the blood-brain barrier in sufficient amounts to interfere with CSF methotrexate effect, according to the National Comprehensive Cancer Network 7
For prevention of toxicity with low-dose weekly methotrexate, folic acid 1-5 mg daily (except on methotrexate day) or leucovorin 10 mg twice daily for 3 days after methotrexate may be administered, as suggested by the Mayo Clinic and the European League Against Rheumatism 7, 8, 9

Patients with third-space fluid collections (pleural effusions, ascites) require lower thresholds for leucovorin escalation, as recommended by the National Comprehensive Cancer Network 7